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<HTML>
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<TITLE>blockmean</TITLE>
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<H1>blockmean</H1>
<HR>
<PRE>
<!-- Manpage converted by man2html 3.0.1 -->
blockmean - filter to block average (x,y,z) data by L2
norm
</PRE>
<H2>SYNOPSIS</H2><PRE>
<B>blockmean</B> [ <I>xyz[w]file(s)</I> ] <B>-I</B><I>x</I><B>_</B><I>inc</I>[<B>m|c</B>][/<I>y</I><B>_</B><I>inc</I>[<B>m|c</B>]]
<B>-R</B><I>west/east/south/north</I>[<B>r</B>] [ <B>-C</B> ] [ <B>-F</B> ] [ <B>-H</B>[<I>nrec</I>] ] [ <B>-L</B>
] [ <B>-S</B> ] [ <B>-V</B> ] [ <B>-W</B>[<B>io</B>] ] [ <B>-:</B> ] [ <B>-bi</B>[<B>s</B>][<I>n</I>] ] [ <B>-bo</B>[<B>s</B>] ]
</PRE>
<H2>DESCRIPTION</H2><PRE>
<B>blockmean</B> reads arbitrarily located (x,y,z) triples [or
optionally weighted quadruples (x,y,z,w)] from standard
input [or <I>xyz[w]file(s)</I>] and writes to standard output a
mean position and value for every non-empty block in a
grid region defined by the <B>-R</B> and <B>-I</B> arguments. Either
<B>blockmean</B>, <B><A HREF="blockmedian.html">blockmedian</A></B>, or <B><A HREF="blockmode.html">blockmode</A></B> should be used as a
pre-processor before running <B><A HREF="surface.html">surface</A></B> to avoid aliasing
short wavelengths. These routines are also generally use
ful for decimating or averaging (x,y,z) data. You can mod
ify the precision of the output format by editing the
D_FORMAT parameter in your .gmtdefaults file, or you may
choose binary input and/or output using single or double
precision storage.
<I>xyz[w]file(s)</I>
3 [or 4] column ASCII file(s) [or binary, see <B>-b</B>]
holding (x,y,z[,w]) data values. [w] is an optional
weight for the data. If no file is specified,
<B>blockmean</B> will read from standard input.
<B>-I</B> <I>x</I><B>_</B><I>inc</I> [and optionally <I>y</I><B>_</B><I>inc</I>] is the grid spacing.
Append <B>m</B> to indicate minutes or <B>c</B> to indicate sec
onds.
<B>-R</B> <I>west,</I> <I>east,</I> <I>south,</I> and <I>north</I> specify the Region of
interest. To specify boundaries in degrees and min
utes [and seconds], use the dd:mm[:ss] format.
Append <B>r</B> if lower left and upper right map coordi
nates are given instead of wesn.
</PRE>
<H2>OPTIONS</H2><PRE>
TP <B>-C</B> Use the center of the block as the output location
[Default uses the mean location].
<B>-F</B> Block centers have pixel registration. [Default:
grid registration.] (Registrations are defined in
GMT Cookbook Appendix B on grid file formats.) Each
block is the locus of points nearest the grid value
location. For example, with <B>-R</B>10/15/10/15 and and
<B>-I</B>1: with the <B>-F</B> option 10 <= (x,y) < 11 is one of
25 blocks; without it 9.5 <= (x,y) < 10.5 is one of
36 blocks.
defaults file. If used, <B><A HREF="GMT.html">GMT</A></B> default is 1 header
record. Not used with binary data.
<B>-L</B> Indicates that the x column contains longitudes,
which may differ from the region in <B>-R</B> by [multi
ples of] 360 degrees [Default assumes no periodic
ity].
<B>-S</B> Report the sum of all z-values inside a block
[Default reports mean value].
<B>-V</B> Selects verbose mode, which will send progress
reports to stderr [Default runs "silently"].
<B>-W</B> Weighted modifier[s]. Unweighted input and output
has 3 columns x,y,z; Weighted i/o has 4 columns
x,y,z,w. Weights can be used in input to construct
weighted mean values in blocks. Weight sums can be
reported in output for later combining several
runs, etc. Use <B>-W</B> for weighted i/o, <B>-Wi</B> for
weighted input only, <B>-Wo</B> for weighted output only.
[Default uses unweighted i/o]
<B>-:</B> Toggles between (longitude,latitude) and (lati
tude,longitude) input/output. [Default is (longi
tude,latitude)]. Applies to geographic coordinates
only.
<B>-bi</B> Selects binary input. Append <B>s</B> for single precision
[Default is double]. Append <I>n</I> for the number of
columns in the binary file(s). [Default is 3 (or 4
if <B>-W</B> is set)].
<B>-bo</B> Selects binary output. Append <B>s</B> for single preci
sion [Default is double].
</PRE>
<H2>EXAMPLES</H2><PRE>
To find 5 by 5 minute block means from the ASCII data in
hawaii.xyg, try
blockmean hawaii.xyg <B>-R</B>198/208/18/25 <B>-I</B>5<B>m</B> > hawaii_5x5.xyg
</PRE>
<H2>SEE ALSO</H2><PRE>
<I><A HREF="blockmedian.html">blockmedian</A></I>(l), <I><A HREF="blockmode.html">blockmode</A></I>(l), <I><A HREF="gmtdefaults.html">gmtdefaults</A></I>(l), <I>gmt</I>(l),
<I><A HREF="nearneighbor.html">nearneighbor</A></I>(l), <I><A HREF="surface.html">surface</A></I>(l), <I><A HREF="triangulate.html">triangulate</A></I>(l)
</PRE>
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